The present invention generally pertains to optical systems and methods and is particularly directed to providing an at least partially in-focus image of a feature at which a person is gazing. Gazing at a feature means perceiving a combined left-eye and a right-eye representation of the feature. A feature can be virtual and does not have to exist in real space. An "in-focus image of a feature" is a clear one-eye or two-eye representation of the feature.
U.S. Pat. No. 5,359,444 describes auto-focusing eyeglasses including lenses containing liquid crystal nematic materials with variable refractive indexes which change in response to a voltage applied across the liquid crystal lens materials. The applied voltage changes the refractive index in accordance with a measured distance to a feature at which a person is gazing so that the lenses are automatically focused as the person gazes at different features that are different distances away. The distance is measured by an infrared ranging system mounted on the frame of the eyeglasses; and the voltage applied across the liquid crystal lens materials is adjusted in accordance with the distance measurement determined by processing an infrared ranging signal with a microprocessor built into the frame of the eyeglasses. A cornea tracking system is used to measure the orientation of the eye by an infrared signal reflected from the cornea in order to provide a fine signal, which in combination with the ranging signal provides information about the temporal location of the line of vision. In operation, a person wearing the eyeglasses faces the feature at which he is gazing in order to point the eyeglasses at such feature, whereupon the focus of the lenses is automatically regulated in accordance with the measured distance to the feature as determined by processing the infrared ranging signal provided by the infrared ranging system mounted on the frame of the eyeglasses.